This meant there were far fewer prepositions in Old English than in Modern English. Instead Old English words were synthesised with suffixes.

In addition, many consonants of Old English have evolved into other, or different consonants in Modern English, many vowels moved from long to short (Great Vowel Shift) and there were some sounds such as a glottal stop (/./) that are heard in only few dialects of English today.

Old English was also influenced in domestic vocabulary and pronouns by Old Norse (a North Germanic language), due to Viking invasions of England (or Aengleland) several centuries after the Aenglish settlement of Britain (Pridain).

A useful text for further reading:

Barber, Charles (1993) The English Language A Historical Introduction Cambridge: The Cambridge University Press

Old English was the language, spoken in what we today call England, roughly between 450 and 1100.
In 449 king Vortigern called foreign mercenaries - the best known being Hengist (also pronounced "Hengest") and Horsa - onto the island to help him fight invaders from Northern Britain.
Inviting these Jutes onto the island wasn't such a good idea after all. Vortigerns actions paved the way for an invasion by the Saxons, the Jutes and the Angles, all of which came from the German mainland. Factors such as Attila the Hun's invasion of the European mainland, changes in climate etc. forced these Germanic tribes to leave their countries. Contrary to common believe they didn't leave as a united invasion force - they arrived in many small groups and founded small kingdoms all over the island.

The Angles, the Saxons and the Jutes of course also brought their own languages. The languages spoken on the island prior to the conquerors' arrival were soon marginalized and suppressed. Some dialects such as Briton (spoken in what is today called Wales and in Cornwall) and Gaelic (spoken in Scotland and Ireland) managed, however, to survive over several centuries and can still be found today (execpt for Cornish which vanished in the late 19th century).

It was an almost impossible task to unite the many small kingdoms to a better manageable country. Only two great rulers achieved this task and became ruler over all of Britain. The first being Offa of Mercia. He successfully fought the Scandinavian landing troops in the North East of the island (having a common enemy obviously greatly helped him on his way to become ruler of Britain). After his death, Mercia soon lost its influence and the political and cultural centre of the island slowly shifted to the Southwest, to Wessex.
King Alfred of Wessex, again, managed to united the kingdoms. He can't, however, be called ruler over all of Britain for an obvious reason: In the North East of the island the Danelaw had been established - a region under the control of the Danish settlers.
Alfred's rule was the beginning of what can be called the "Golden Age of Britain". Britain was an economic power that shouldn't be underestimated. As some findings in the Sutton Hoo burial ship show, Britain sustained trading relations reaching as far as Greece.

Concerning the Old English language, Wessex played a unifying role. Out of the several dialects spoken on the island at that time, the West Saxon dialect emerged as a standard.
What we today call "Old English" is in fact that West Saxon dialect.

Until 597 - the year Pope Gegory's missionary Augustine arrived on the island - Old English was hardly written. The spread of Christianity rapdidly changed that. Several works of the Old English period survived until the present day. Authors such as the Bede (673-735) (who, in 631, wrote the Historia Ecclesiastica) provided the generations to come with invaluable historical and social facts about that time.

On a linguistical level, Old English varies greatly from Modern English. It was an entirely Germanic language, resembling Modern German much more than the English spoken today. To illustrate the differences in word order, gender system etc. I've literally translated a short passage of Beowulf into Modern English:

ða com of more under misthleoþum
there came (out) of the moorland under (the) mistcovered hills

sumne besyrwan/ in sele þam hean.
some to surprise in (the) hall the high.

(There came out of the moorland under the mistcovered
hills Grendel, god's wrath bearing;
He had in mind to surprise some humans in Heorot
(king Hrothgars "high hall")

The passage shows several important OE elements:

sele -> the "-e" Suffix marks the dative

Adjectives are declined according to the (also declined) noun's gender, case and number. The genders being feminine, maculine and neutral. The cases still exist in Modern English, although most speakers don't notice them as the markers have mostly vanished.

manscaðda -> A so called Kenning - a metaphor with a not totally obvious meaning. Here: "The one who despises mankind"

Most poems of that period, including Beowulf, were written in a rhyme scheme called "Alliteration".
Each line of the poem consits of two parts, divided by the caesura. Each part contains two stresses and may contain several unstressed elements. The first element after the caesura is considered rhyme forming - it alliterates with a corresponding element within the first part.